A typical boat lift for smaller recreational type boats comprises a frame which is installed in water which is adjacent a shore of a body of water such as a lake. The boat lift has a frame comprising upright posts which are arranged at locations around a perimeter of the frame and which typically have large feet enabling the frame to sit on the bed of the body of water. The uprights are spaced apart so that a boat can enter and exit space bounded by the frame perimeter. The frame supports an elevator for vertical or cantilever raising and lowering of a boat within that space. The elevator comprises a lift platform providing underlying support for a hull of a boat, and a mechanism for raising and lowering the lift platform.
One example of such a mechanism comprises a gear box mounted on the frame. The gear box has an input shaft and an output shaft. The output shaft is coupled to the lift platform by a system which includes pulleys and cables. The gearbox provides a mechanical advantage which multiplies torque being applied to the input shaft so that greater torque is developed at the output shaft when torque is being applied to the input shaft in a direction for vertical or cantilever raising of the lift platform. The gearbox reduces torque being applied by the weight of the boat on the lift platform as the boat is being lowered although the mere weight of the boat on the lift platform is insufficient to cause the output shaft to rotate due to a brake-like clutch.
Raising and lowering of the lift platform may be performed manually and/or electrically. A large diameter hand wheel coupled to the input shaft can be manually turned in one direction to raise the lift platform and in the other direction to lower the lift platform.
A bidirectional electric motor, either AC or DC can be used to raise and lower the lift platform.